Which of the following outlines the overall sequence of events in the complete oxidation of glucose?

Question

BlackTom AI · Accepted Answer

Glycolysis converts one glucose molecule (6C) into two pyruvate molecules (3C each) in the cytosol, so glycolysis is the first step in complete glucose oxidation.

1. Relevant knowledge points and concepts
- Glycolysis (cytosol): glucose → 2 pyruvate, net 2 ATP, 2 NADH.
- Pyruvate oxidation (mitochondrial matrix): 2 pyruvate → 2 acetyl-CoA + 2 CO2 + 2 NADH (overall for one glucose).
- Tricarboxylic acid (TCA) cycle / citric acid cycle (mitochondrial matrix): each acetyl-CoA → 3 NADH + 1 FADH2 + 1 GTP + 2 CO2; for glucose (2 acetyl-CoA) this yields 6 NADH, 2 FADH2, 2 GTP, 4 CO2.
- Electron transport chain (ETC) and oxidative phosphorylation (inner mitochondrial membrane): NADH and FADH2 donate electrons to the ETC; proton gradient drives ATP synthase; O2 is the final electron acceptor, forming H2O.

2. Step-by-step reasoning process
- Glucose is first broken down in glycolysis to produce pyruvate and reduce electron carriers (NADH). Pyruvate cannot enter the TCA cycle directly; it is converted to acetyl-CoA (link reaction) inside mitochondria.
- Acetyl-CoA enters the TCA cycle, where carbon atoms are fully oxidized to CO2 while more electron carriers (NADH, FADH2) and GTP/ATP are produced.
- The electron carriers generated (from glycolysis, pyruvate oxidation, and TCA) are oxidized in the ETC; their electrons flow through complexes to O2, producing water and driving ATP synthesis.

3. Intermediate “calculations” (summary per glucose)
- Glycolysis: net +2 ATP, +2 NADH, 2 pyruvate.
- Pyruvate → acetyl-CoA (x2): +2 NADH, +2 CO2.
- TCA (2 acetyl-CoA): +6 NADH, +2 FADH2, +2 GTP, +4 CO2.
- ETC uses these NADH/FADH2 to produce bulk ATP.

4. Why the correct answer is correct
The only sequence that follows the biochemical order of carbon breakdown and electron flow is: glycolysis → TCA cycle (after pyruvate conversion to acetyl-CoA) → electron transport chain. This sequence reflects where substrates are produced and where the reducing equivalents are consumed to make ATP.

5. Why other options are incorrect
- "electron transport chain, TCA cycle, Cori cycle": ETC cannot precede production of NADH/FADH2 and includes the Cori cycle (lactate shuttle) which is not part of complete oxidation.
- "Cori cycle, TCA cycle, glycolysis": Cori cycle operates under anaerobic conditions and does not outline full oxidation; glycolysis occurs before TCA, not after.
- "TCA cycle, electron transport chain, glycolysis": Glycolysis occurs first in the cytosol to generate pyruvate; it cannot come after the TCA.

6. Conclusion / final confirmation
The correct overall sequence is glycolysis, TCA cycle, electron transport chain, which matches the provided answer: glycolysis, TCA cycle, electron transport chain.

Which of the following outlines the overall sequence of events in the complete oxidation of glucose?单项选择题

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